Since their identification as disease-causing agents of animals and more recently of humans, it is now apparent that most retroviruses are neurotropic to varying degrees. Mechanisms by which retroviruses induce neurologic disease are, however, currently both poorly understood and the subject of intense research interest. This project is intended to provide sufficient support for research training in neurobiology and retrovirology to enable the candidate, Steven W. Dow, to investigate mechanisms by which retroviruses infect and alter function of neural cells. The investigations proposed will utilize both in vitro and in vivo systems and molecularly cloned feline retroviruses (feline leukemia virus {FeLV} and feline immunodeficiency virus {FIV}) to develop models for study of retrovirus- induced neurologic disease. The specific aims of Phase 1 of the work are: 1) to develop methods for primary culture and characterization of feline CNS cells; 2) to identify central nervous system (CNS) target cells for retrovirus infection; and 3) to use in vitro and in vivo assays to identify and analyze potentially neurotropic retroviruses. Techniques will be developed for culture of enriched populations of the three major classes of neural cells: astrocytes, oligodendrocytes, and neurons. Immunocytochemical techniques will be used to identify the time course and susceptibility of cultured feline CNS cells to feline retrovirus infection in vitro after exposure to either cell-free virus or to virus-infected mononuclear cells. Correlative in vivo studies will use in situ hybridization and immunocytochemistry to identify infected cells in CNS tissues of retrovirus-inoculated cats. Potentially neurotropic and/or neurovirulent strains of feline retroviruses will be examined for their differential ability to infect and/or induce alterations in cultured feline CNS cells. In Phase 2, these investigations will be extended to include identification of CNS cell surface receptors that mediate retrovirus attachment and to characterize retrovirus-induced alterations in neural cell function. Studies to evaluate alterations in cell function will include immunocytochemical identification of altered expression of cell surface and differentiation antigens in infected glial cells, morphologic studies of survival and outgrowth characteristics of neurons, and measurement of pituitary hormone secretion (anterior pituitary cells). In vivo studies, to be ongoing during the training period, will correlate the in vitro and in vivo neurotropism of feline retroviruses by determining whether viruses that are neurotropic for cultured feline CNS cells are also able to induce neurologic disease in cats after intracisternal inoculation.